Zimbabwe's Foreign Minister Simbarashe Mumbengegwi summoned U.S. Ambassador Christopher Dell to his office early Wednesday and handed him a diplomatic note of protest. The diplomatic tension between the two countries follows Mr. Dell's statement last week that Zimbabwe's economic and social crisis is caused by government mismanagement.

Mr. Dell was handed the protest note by Zimbabwe's foreign minister and the U.S. embassy in Harare has not disclosed its contents.

The U.S. embassy responded by saying that the ambassador reserved his right to make an appropriate reply to the diplomatic note after he has had consultations with the U.S. State Department in Washington.

Mr. Dell has attracted unprecedented criticism, personal attacks and threats by the government since he made a speech last week at a U.S.-backed university in eastern Zimbabwe. In his remarks, Mr. Dell said Zimbabwe's economic and humanitarian crisis was self-inflicted.

He told students and staff at the public lecture that, "The Zimbabwe government's own gross mismanagement of the economy and its corrupt rule has brought on the crisis."

The state controlled media, which largely reflects Zimbabwe government thinking has speculated that the U.S. ambassador would be expelled.

On Tuesday, president Robert Mugabe told state journalists that Mr. Dell "could go to hell."

Zimbabwe's foreign minister has accused Mr. Dell of "undiplomatic behavior," and expressed the government's extreme displeasure over his activities in Zimbabwe.

Mr. Mumbengegwi accused the U.S. ambassador of seeking confrontation with Zimbabwe. He said the Zimbabwe government was left with what he called, "no other conclusion except that the ambassador has deliberately decided to go on a confrontational course which the government takes seriously and will not tolerate."

Last month Ambassador Dell was detained by the presidential guard while he was walking his dog in the National Botanical Gardens which is close to Mr. Mugabe's official residence.

Since 2002, the United States has provided more than $300 million of food aid to Zimbabwe and is the biggest bilateral donor of HIV AIDS assistance.

Zimbabwe's agriculture based economy has crashed over the last six years since Mr. Mugabe began expelling white commercial farmers from land that once produced 40 percent of the country's annual foreign exchange.